Liquid crystal polymer shrinks SMD transformers

Edited by the Engineeringtalk editorial team Sep 2, 2003

Epcos chose DuPont Zenite LCP for its coil formers for SMD transformers used in telecommunications equipment such as splitters and line transformers.

Epcos chose DuPont Zenite LCP for its coil formers for SMD transformers used in telecommunications equipment such as splitters and line transformers.

Epcos, a major developer and manufacturer of leading-edge electronic components, chose this liquid crystal polymer for its optimal combination of properties, which include high dielectric strength and thermal resistance, and very good melt-flow.

These characteristics are essential for making miniaturised electronic components for mounting on circuit boards with SMD technology.

The growing use of digital subscriber line (DSL) technology, which is expected to increase further with video-on-demand, teleworking and telelearning, requires an increased bandwidth for signal transmission between Internet service providers' central offices and customer premises.

Epcos' specially developed EPX and EPO core geometries, made of T66 and T57 ferrite materials, offer good data transmission rates combined with greater miniaturisation.

For making the coil formers for these applications, Munich-based Epcos uses Zenite 7130.

This glass-fibre-reinforced LCP combines good toughness with a heat deflection temperature of 289C and high dimensional stability.

Containing no halogen additives, the material is recognised by Underwriters Laboratories as UL94V0 at 0.75 mm.

Processing this LCP is less costly than working with thermosetting resins, because the melt sets rapidly and injection-moulded parts of Zenite do not need to be deflashed.

LCPs in general are highly suitable for the cost-efficient manufacture of many electrical and electronic components for the automotive, telecommunications and aerospace industries.

Josef Sedlmeier, Ferrite Components Project Leader at Epcos, comments: "Thanks to the good melt-flow properties of Zenite, we can injection-mould very fine coil formers with a wall thickness of less than 0.4mm and a footprint of 25mm2.

With the high strength and impact resistance of this LCP, these precision parts are nevertheless robust enough to withstand the stresses that occur during coil winding.

The high thermal deflection temperature of Zenite 7130 means that parts can withstand temperature peaks of up to 260C, which occur during reflow-soldering, when the complete transformers are mounted on the circuit board".

"Our new ferrites allow SMD transformers to be miniaturised without compromising their performance", Sedlmeier continues.

"This means, for example, that more ADSL interface transformers can be mounted per unit of PCB real estate; this in turn helps to lower per-connection costs at the switching centre".

Epcos' EP range of SMD transformers, designed for an operating voltage of 250V (test voltage 1500V) meet international standards for telecommunications applications, such as EN60950, IEC950, UL1950/CSA950 and AS/NZS3260.

Typical applications for these ferrite transformers are highpass and lowpass filters, impedance matching and electrical insulation transformers.